Electron ionization source and methods of using the same

Abstract

An electron ionization source including at least one gas source assembly having at least one nozzle having at least one outlet configured to deliver at least one analyte material into at least one ionization region, at least one electron source assembly configured to generate at least one electron beam intersecting the ionization region, and at least one fixture configured to positionally secure the gas source assembly such that the outlet of the nozzle is aligned relative to the electron beam, the fixture comprises a first jaw defining a clamping space to receive a clamping section of the gas source assembly, a second jaw movably coupled to the first jaw and configured to clamp the clamping section within the clamping space, wherein one or more fasteners may be operated to adjust the vertical position of the gas source assembly along at least one of the x-axis, y-axis, and / or z-axis within the clamping space, wherein the gas source assembly may be alignable in three dimensions relative to the electron beam and to an inlet of a vacuum pump positioned downstream of the ionization region.

Description

ELECTRON IONIZATION SOURCE AND METHODS OF USING THE SAMECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present patent application claims priority to U.S. Prov. Pat. App. Ser. No. 63 / 664,747, filed on June 27, 2024, entitled "ELECTRON IONIZATION SOURCE AND METHODS OF USING THE SAME," the contents of which are incorporated by reference in its entirety herein.TECHNICAL FIELD

[0002] Embodiments of the devices disclosed herein relate generally to electron ion sources and, more particularly, to electron ionization sources with improved alignment, serviceability, and configurational aspects, and methods of operating the same.BACKGROUND

[0003] Electron ionization sources create ions from the interaction of energetic electrons (produced through thermionic emission by heating a wire filament having an electric current running through it) with gaseous material (i.e., solid- or gas-phase atoms or molecules). Electron ionization sources are often used to form ions for devices such as analyzers (e.g., optical emission spectrometers, residual gas analyzers, gas chromatographs, etc.), ionization gauges (e.g., hot cathode ionization gauges), and the like. While currently available electron ionization sources have proven useful, a number of shortcomings have been identified. Performance of the electron ionization source may be compromised if the electron beam is not aligned relative to the ionization region of the device. Aligning the electron beam relative to the ionization region can be a time-consuming process during manufacture and when installed.

[0004] In light of the foregoing, there is an ongoing need for an electron ionization source which is capable of having the ability to easily align electron beam relative to the ionization region during manufacture and once installed on a device.SUMMARY

[0005] The present application discloses various embodiments of an electron ionization source and methods of using the same. In one embodiment, the present application discloses an electron ionization source. The electron ionization source includes at least one gas source assembly. The gas source may include at least one nozzle having at least one outlet configured to deliver at least one gaseous analyte material into at least one ionization region. At least oneelectron source assembly may be included in the electron ionization source and may be configured to generate at least one electron beam intersecting the ionization region. The electron ionization source may include at least one fixture configured to positionally secure the gas source assembly such that the outlet of the nozzle is aligned relative to the electron beam path. In one embodiment, the fixture comprises a first jaw defining a clamping space to receive a clamping section of the gas source assembly, a second jaw movably coupled to the first jaw and configured to clamp the clamping section within the clamping space. One or more fasteners may be operated to adjust the vertical position of the gas source assembly along at least one of the x-axis, y-axis, and / or z-axis within the clamping space. As such, the gas source assembly may be alignable in three dimensions relative to the electron beam and to an inlet of a vacuum pump positioned downstream of the ionization region. In one embodiment, the position of the ionization region may be adjusted such that ionization region is aligned relative to the electron beam. In another embodiment, the position of the electron beam may be adjusted such that the electron beam is aligned relative to the ionization region.

[0006] In addition, the present application discloses a method of adjusting a nozzle in an electron ionization source which includes inserting a clamping section of a gas source assembly into a clamping space defined by a first jaw of a fixture. Thereafter, positioning the gas source assembly within the clamping space to align an outlet of a nozzle along at least one of an x-axis, y-axis, or z-axis relative to an ionization region. A second jaw may be actuated to engage the clamping section by tightening one or more fasteners to bias the clamping section against the first jaw and secure the position of the nozzle. Thereafter, the outlet of the nozzle may be aligned such that a gas delivery axis is aligned with a direction of an electron beam generated by an electron source assembly and / or an inlet of a vacuum pump downstream of the ionization region.

[0007] Other features and advantages of electron ionization source and methods for use will become apparent from a consideration of the following detailed description.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The drawings disclose illustrative embodiments and are not intended to set forth all embodiments of the electron ionization source and methods for use. Details that may be apparent or unnecessary may be omitted to save space or for more effective illustration. Conversely, some embodiments may be practices without all the detailed disclosed with regardto specific embodiments. When the same reference numbers appear in different drawings, the reference numbers refer to same or similar components or steps. The novel aspects of the electron ionization source and methods for use as disclosed herein will become more apparent by consideration of the following figures, wherein:

[0009] FIGS. 1 and 2 illustrate perspective views of an embodiment of an electron ionization source;

[0010] FIG. 3 illustrates another perspective view of the embodiment of the electron ionization source shown in FIGS. 1 and 2, with the repelling electrode shown in FIGS. 1 and 2 removed to facilitate better viewing of the ionization region of the electron ionization source;

[0011] FIG. 4 illustrates a cross-section view of the embodiment of the electron ionization source shown in FIGS. 1 to 3, taken along line IV-IV shown in FIG. 1, with the repelling electrode removed to facilitate better viewing of the ionization region;

[0012] FIG. 5 illustrates an exploded perspective view of a portion of the gas source assembly shown in FIGS. 1 to 4;

[0013] FIG. 6 illustrates a perspective view of a front side of the embodiment of the electron source assembly in the electron ionization source shown in FIGS. 1 to 4, according to one embodiment;

[0014] FIG. 7 illustrates a perspective view of a rear side of the embodiment of the electron source assembly shown in FIG. 6;

[0015] FIG. 8 illustrates an enlarged perspective view of the embodiment of the alignment electrodes and filament shown of the electron source assembly shown in FIGS. 6 and 7; and

[0016] FIGS. 9 to 11 illustrate perspective views of an electrode for use with an embodiment of an electron source assembly.DETAILED DESCRIPTION

[0017] Example embodiments are described herein with reference to the accompanying FIGS. Unless otherwise expressly stated, in the drawings the sizes, positions, etc., of components, features, elements, etc., as well as any distances therebetween, are not necessarily to scale, but are exaggerated for clarity.

[0018] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearlyindicates otherwise. It should be recognized that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range, as well as any sub-ranges therebetween. Unless indicated otherwise, terms such as "first," "second," etc., are only used to distinguish one element from another. For example, one node could be termed a "first node" and similarly, another node could be termed a "second node", or vice versa. The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0019] Unless indicated otherwise, the term "about," "thereabout," "substantially," etc., means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art.

[0020] Spatially relative terms, such as "below," "beneath," "lower," "above," and "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature, as illustrated in the FIGS. It should be recognized that the spatially relative terms are intended to encompass different orientations in addition to the orientation depicted in the FIGS. For example, if an object in the FIGS, is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. An object may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly.

[0021] Many of the FIGS, illustrate x-, y-, and / or z-axes. Unless otherwise specified, the x-, y-, and z-axes variously illustrated in the FIGS, are of the same coordinate system. Accordingly, it should be appreciated that an arrow representing a particular axis (e.g., the x-axis) illustrated in one FIG. represents the same axis illustrated in another FIG. even though the two FIGS, illustrate the particular axis oriented in different directions.

[0022] Like numbers refer to like elements throughout. Thus, the same or similar numbers may be described with reference to other drawings even if they are neither mentioned nor described in the corresponding drawing. Also, even elements that are not denoted by reference numbers may be described with reference to other drawings.

[0023] It will be appreciated that many different forms and embodiments are possible without deviating from the spirit and teachings of this disclosure and so this disclosure should not be construed as limited to the example embodiments set forth herein. Rather, these examples and embodiments are provided so that this disclosure will be thorough and complete, and will convey the scope of the disclosure to those skilled in the art.A. General Discussion of Embodiments Concerning an Electron Ionization Source

[0024] FIGS. 1 and 2 illustrate perspective views of an embodiment of an electron ionization source. In particular, FIGS. 1 and 2 illustrate the electron ionization source from opposite sides thereof. FIG. 3 illustrates another perspective view of the electron ionization source shown in FIGS. 1 and 2, with the repelling electrode (i.e. the repelling electron repels ions formed int he ionization region) removed to facilitate better viewing of the ionization region. FIG. 4 illustrates a cross-section view of the electron ionization source shown in FIGS. 1 and 2, taken along line IV- IV shown in FIG. 1, with the repelling electrode removed to facilitate better viewing of the ionization region.

[0025] Referring to FIGS. 1 and 2, an electron ionization source, such as electron ionization source 100, includes a gas source assembly 102, a first electron source assembly 104a and a second electron source assembly 104b, a first filament electron entrance electrode 106, a second filament electron entrance electrode 108, an ion repelling electrode 110, an ion exit electrode or ion extracting plate 112 and a lens electrode 114. A region within the electron ionization source 100, defined between the first filament electron entrance electrode 106, the second filament electron entrance electrode 108, the ion repelling electrode 110 and the ion exit electrode 112, is referred to herein as an "ionization region." As used herein, the first filament electron entrance electrode 106, the second filament electron entrance electrode 108, the ion repelling electrode 110 and the ion exit electrode 112 can be each generically (and collectively) referred to herein as "ionization region electrodes." Although the electron ionization source 100 is described herein as including first and second electron source assemblies 104a and 104b (each also generically referred to herein as an "electron source assembly 104"), it will be appreciated that the electron ionization source 100 may include onlythe first electron source assembly 104a or the second electron source assembly 104b. In one embodiment, the two electron source assemblies 104a, 104b may be used individually or may be operated simultaneously.

[0026] Although not shown in FIGS. 1 and 2, the electron source assembly 104 includes an electrode support member configured to hold one or more alignment electrodes, also of the electron source assembly 104; both the electrode support member and the alignment electrodes will be discussed in greater detail with respect to FIGS. 6 to 8. Although not shown, the electron ionization source 100 may, in an optional embodiment, include a trap electrode (e.g., a metal plate, at ground potential) arranged opposite an electron source assembly 104 to collect the electrons generated by the electron source assembly 104 exiting the ionization region. In another embodiment, in which the electron ionization source 100 includes first and second electron source assemblies 104a and 104b, one or more alignment electrodes (discussed in greater detail below) of one of the electron source assemblies 104 can be a trap electrode while the other of the electron source assemblies 104 is operated to generate the electrons.

[0027] As best shown in FIGS. 1 to 3, the first filament electron entrance electrode 106, second filament electron entrance electrode 108, ion exit electrode 112, lens electrode 114 and mounting flange 101 are mechanically coupled together by a plurality of fastener assemblies 107 (e.g., each comprised of a bolt or screw and a plurality of spacers and / or washers).Likewise, the first filament electron entrance electrode 106, second filament electron entrance electrode 108, and ion repelling electrode 110 can be mechanically coupled together by a plurality of fastener assemblies 109 (e.g., each comprised of a bolt or screw and a plurality of spacers and / or washers).

[0028] As also shown in FIGS. 1 to 3, the electron ionization source 100 may include a mounting flange 101 to facilitate coupling of the electron ionization source 100 to a mass analyzer (e.g., a quadrupole mass analyzer, time of flight mass analyzer, magnetic sector, etc.) (not shown). The mounting flange 101 includes an electrically grounded mounting plate 103 (e.g., to facilitate mechanical coupling to the other components of the electron ionization source 100) and sleeve 105 extending from the mounting plate 103, to which the analyzer can be coupled. The mounting plate 103 includes an outlet bore (see, e.g., 400 in FIG. 4) permitting ions generated within the ionization region to enter into the analyzer.

[0029] The gas source assembly 102 is configured to deliver a gaseous analyte from a nozzle 118 thereof to enter into the ionization region (e.g., primarily along an analyte delivery axis100a, in the +z direction). As best shown in FIG. 4, the gas source assembly 102 includes a main body 402 having a channel with an inlet port 404 in fluid communication with an outlet of the nozzle 118, which is coupled to the main body 402. Accordingly, gaseous analyte enters into the channel of the main body 402 at the inlet port 404 and is conveyed to the nozzle 118 through the channel as indicated by the dashed-line arrows. The gaseous analyte thereafter exits the gas source assembly 102 at an outlet orifice of the nozzle 118.

[0030] Each of the first and second electron source assemblies 104a and 104b, respectively, is located outside the ionization region, behind a respective one of the first filament electron entrance electrode 106 or the second filament electron entrance electrode 108, and is configured to generate a beam of electrons (also referred to herein as an "electron beam") that traverses the ionization region. For example, the first electron source assembly 104a is configured to generate a beam of electrons that traverses the ionization region, e.g., in the +x direction, as indicated by dashed arrow 100b. Similarly, the second electron source assembly 104b is configured to generate a beam of electrons that traverses the ionization region in the -x direction.

[0031] Each of the first filament electron entrance electrode 106 and second filament electron entrance electrode 108 have main surfaces that face toward (and are exposed to) the ionization region. The first filament electron entrance electrode 106 and second filament electron entrance electrode 108 are arranged such that the main surfaces are at least substantially parallel to one another. The first filament electron entrance electrode 106 includes a first electrode aperture 106a (see, e.g., FIGS. 3 and 4) arranged so as to permit electrons generated by the first electron source assembly 104a to enter into the ionization region. Likewise, the second filament electron entrance electrode 108 includes a second electrode aperture 108a (see, e.g., FIG. 1) arranged so as to permit electrons generated by the second electron source assembly 104b to enter into the ionization region. The relative arrangement of the first and second electron source assemblies 104a and 104b, respectively (as well as the relative arrangement of the first and second electrode apertures 106a and 108a, respectively), are provided such that the beam of electrons generated by the first electron source assembly 104a are transmittable through the second electrode aperture 108a to exit the ionization region and such that electrons generated by the second electron source assembly 104b are transmittable through the first electrode aperture 106a to exit the ionization region.

[0032] The ion repelling electrode 110 is configured to repel ions generated within the ionization region toward the aforementioned outlet bore 400 of the electron ionization source 100 through an exit aperture in the ion exit electrode 112 (shown, but not labelled in FIGS. 1 to 3). With the ion exit electrode 112, the lens electrode 114 focuses and extracts the generated ions through a lens aperture formed therein (shown, but not labelled in FIGS. 1 to 3) and transmits the ions through the outlet bore 400 to the analyzer. The exit aperture and lens aperture are shown in FIG. 4, and labeled therein at 404 and 406, respectively.

[0033] The electron ionization source 100 may be arranged within a vacuum chamber (not shown) that can be maintained at a chamber pressure that is relatively low compared to a pressure with which the analyte is introduced into the ionization region from the outlet of the nozzle 118 (e.g., during operation of the electron ionization source 100). For example, the chamber pressure can be maintained at 2E-5 Torr or less whereas pressure with which the analyte is delivered into the ionization region from the outlet of the nozzle 118 can be 1 E-4 Torr or greater. A vacuum pump (not shown) is provided to maintain the chamber pressure by any suitable or known technique. Generally, the inlet of the vacuum pump arranged so as to be coaxial or otherwise suitably aligned to the analyte delivery axis 100a so that at least the majority of any non-ionized analyte within the ionization region is removed from the ionization region by the vacuum pump, thereby restricting or preventing backstreaming of the gas.

[0034] During operation of the electron ionization source 100, the analyte delivered into the ionization region from the outlet of the nozzle 118 forms a plume (also referred to herein as an "analyte plume") which freely expands predominantly along the gas delivery axis 100a. Transverse to the analyte delivery axis 100a, the plume freely expands in a manner approximating a cosine distribution. As used herein, a plume that "freely expands" expands with substantially no collisions, or very few collisions, occurring between atoms or molecules of the analyte material or between analyte material and various surfaces exposed to the ionization region. Simultaneous with delivery of analyte into the ionization region, an electron source assembly 104 (i.e., the first electron source assembly 104a, the second electron source assembly 104b or a combination thereof) generates an electron beam, as discussed above, which propagates through the plume to ionize atoms or molecules of the analyte within the plume and generate ions thereby. As will be discussed in greater detail below, the electron beam traverses the analyte plume at a location that is very close to the outlet of the nozzle 118 to assure maximum analyzer sensitivity and minimize the chances for the analyte to thermalize and mixwith background gases. Generally, the electron beam is considered to be "very close" to the outlet of the nozzle 118 when if it is within 5 mm or less (e.g., within 3 mm, within 1 mm, within 0.5 mm, within 0.25 mm, within 0.1 mm or less, etc., or between any of these values) away from the outlet of the nozzle 118. There will likely be a few electrons that stray from the electron beam, and the electron beam will not have a perfect clear-cut edge, so a few electrons may hit the nozzle 118. These factors should be considered to keep the number of electrons that hit the nozzle 118 acceptably low without having to move the main part of the electron beam undesirably far away.

[0035] Appropriate voltages can be applied to the ion repelling electrode 110, ion exit electrode 112 and lens electrode 114 by any suitable or known technique to bias the generated ions in the -y direction (e.g., as indicated by dashed arrow 100c), whereupon the biased ions can enter into the analyzer. Analyte material within the plume that is not ionized is exits the ionization region through the inlet of the vacuum pump.B. Embodiments Concerning Alignment of the Nozzle to the Electron Beam

[0036] According to some embodiments, desirable generation of ions from the analyte material delivered into the ionization region can be facilitated by properly aligning the outlet of the nozzle 118 to the electron beam generated by an electron source assembly 104. Accordingly, the electron ionization source 100 may be configured such that the position of the outlet of the nozzle 118 (e.g., along the y- and / or z-axes as shown in FIG. 1 or 3) is adjustable. The electron ionization source 100 may also be configured such that the outlet of the nozzle 118 can be reliably and repeatedly located at a desired position along the x-axis (as shown in FIG. 1 or 3). Likewise, the electron ionization source 100 can be configured to ensure that the outlet of the nozzle 118 is reliably oriented toward the inlet of the vacuum pump. According to embodiments of the present invention, the electron ionization source 100 may include a fixture 120 configured to facilitate desired positioning of the outlet of the nozzle 118 within the ionization region.

[0037] Generally, fixture 120 may be mechanically fixed to other components of the electron ionization source 100 (e.g., to the electron entrance electrode 106, electron exit electrode 108, and repelling electrode 110) by one or more of the aforementioned fastener assemblies 109, or the like or any combination thereof. For example, the fixture 120 may include one or more tabs (e.g., labeled in FIG. 3 at 300) adapted to be engaged by a respective fastener assembly 109. Asshown in FIGS. 1 to 4, the fixture 120 is provided as a vise having a first jaw 122 and a second jaw 124 movably coupled to the first jaw 122 (e.g., by one or more fasteners 111, such as a threaded bolt).

[0038] As best shown in FIG. 3, the first jaw 122 defines a clamping space dimensioned so as to accommodate a clamping section 126 of the gas source assembly 102. In the illustrated embodiment, the depth of the clamping space (as measured along the z-axis) is slightly less than a corresponding dimension of the clamping section 126 (also measured along the z-axis, as shown in FIG. 3) and, when the second jaw 124 is secured to the first jaw by fastener(s) 111, the second jaw 124 presses against the clamping section 126, thereby biasing the clamping section 126 against the first jaw 122 and holding the gas source assembly 102 within the fixture 120. It will be appreciated, however, that the fixture 120 may be provided as any other device or mechanism suitable for positionally fixing the gas source assembly 102 within the electron ionization source 100.

[0039] Constructed as described above, the fixture 120 can be manipulated to adjust the position of the nozzle 118 along the y-axis. For example, the fasteners 111 may be loosened to allow the clamping section 126 of the gas source assembly 102 to be moved (e.g., raised or lowered) within the clamping space of the first jaw 122, along the y-axis. After the clamping section 126 has been raised or lowered as desired, the fasteners 111 may be tightened to fixedly hold the clamping section 126 within the clamping space.

[0040] To ensure that the nozzle 118 can be reliably and repeatedly positioned at a desired position along the x-axis (e.g., so that the gas delivery axis 100a is coaxial with or otherwise suitably aligned to the aforementioned inlet of the vacuum pump), lateral surfaces of the clamping space in the fixture 120 can be aligned (along the x-axis) to the inlet of the vacuum pump.

[0041] To ensure that the nozzle 118 can be reliably and repeatedly oriented within the x-y plane (i.e., a plane parallel to the x- and z-axes), so that the gas delivery axis 100a is coaxial with or otherwise suitably aligned to the aforementioned inlet of the vacuum pump, one or more exterior surfaces of the clamping section 126 and one or more corresponding surfaces of the first jaw 122 and / or second jaw 124 exposed to the clamping space may have reference surfaces defining lateral surfaces of the clamping space in the fixture 120 can be aligned (along the x-axis) to the inlet of the vacuum pump. For example, one or more pairs of corresponding surfaces of the clamping section 126 and of the clamping space of the first jaw 122 (i.e., surfaces ofclamping section 126 and of the clamping space of the first jaw 122 that contact each other when the gas source assembly 102 is held within the fixture 120) may be generally flat and parallel to the x-y plane (i.e., a plane parallel to the x- and y-axes), to the y-z plane (i.e., a plane parallel to the y- and z-axes), or a combination thereof.

[0042] In one embodiment, positional adjustability of the outlet of the nozzle 118 along the z- axis can, optionally, be provided for by permitting the nozzle 118 to be movable with respect to the main body 402 of the gas source assembly 102. For example, and with reference to FIG. 5, the main body 402 of the gas source assembly 102 may include a nozzle mounting block 500 having a threaded nozzle bore 502 defined therein (e.g., extending from an exterior surface of the nozzle mounting block 500 to the channel of the main body 402). The nozzle 118 may have a threaded nozzle body 504 adapted to be threadedly coupled to the nozzle mounting block 500. Also labelled in FIG. 5 is the outlet of the nozzle 118, identified at 506. The outlet 506 is centered at the rotational axis of the nozzle body 504; accordingly, the location of the outlet 506 along the z-axis may thus be precisely set based on how fully the nozzle body 504 is threaded into the nozzle bore 502.

[0043] In other embodiments, positional adjustability of the outlet of the nozzle 118 along the z-axis can be facilitated by providing one or more set screws (e.g., each extending through the first jaw 122 and into the clamping space of the fixture 120 by an adjustable distance), one or more compression seals (e.g., an O-ring), one or more shims, or the like, or any combination thereof to engage with the clamping section 126 of the gas source assembly 102 and thereby press the clamping section 126 against the second jaw 124.C. Embodiments Concerning Alignment of the Electron Beam to the Nozzle

[0044] According to some embodiments, desirable generation of ions from the analyte material delivered into the ionization region can be facilitated by properly aligning the electron beam generated by an electron source assembly 104 to the outlet of the nozzle 118. Accordingly, the electron source assembly 104 may be configured to selectively and variably steer the electron beam. Steering of the electron beam can also be beneficial if the trajectory of the electron beam is affected by the buildup of contamination that changes the trajectory of ions through the ionization region. Steering of the electron beam can also be beneficial if the position of the nozzle 118 or one or more components of the electron source assembly 104 changes over time (e.g., due to thermal expansion or other mechanical deformation of one or more components of the electron ionization source 100). Generally, and with reference to FIG. 6, the electron sourceassembly 104 may include a filament 600, filament posts 602, a post support 604, filament leads606, alignment electrodes 608 and an electrode support member 610. Referring to FIG. 7, the electron source assembly 104 also includes lead terminals 700.

[0045] Referring to FIGS. 6 and 7, the filament 600 is provided as a wire of any material capable of producing electrons via thermionic emission, as is known in the art. The filament posts 602 are connected to opposite ends of the filament 600 and are electrically conductive so that an electric current may be generated within the filament 600, e.g., from a power supply (not shown). The post support 604 is an electrically insulative body in which the filament posts 602 can be securely held. First ends of each of the filament leads 606 (not shown) are electrically connected to respective ones of the filament posts 602 within the post support 604 and second ends of each of the filament leads 606 are electrically connected to respective ones of the lead terminals 700. Although not shown, the power supply may be electrically connected to the lead terminals 700 so that an electric current may be generated in the filament 600 to generate the electron beam.

[0046] Referring to FIG. 6, the alignment electrodes 608 are spaced apart from one another and are fixedly mounted to the electrode support member 610 (e.g., using an adhesive, clips, clamps, or the like or any combination thereof). For example, the alignment electrodes 608 may be individually and independently mounted to the electrode support member 610, or the alignment electrodes 608 may be secured to a common dielectric carrier (e.g., a ceramic plate) and the carrier may be mounted to the electrode support member 610. Generally, the electrode support member 610 is provided as an electrically insulative body (e.g., a printed circuit board) having a plurality of conductive traces 612 formed thereon. Each of the alignment electrodes 608 is electrically connected to a respective one of the plurality of conductive traces 612 (via solder material, conductive paste, by direct contact, etc.). The conductive traces 612 are also electrically connected to one or more single- or multi-channel power supplies. Accordingly, the conductive traces 612 may transmit electrical energy from the power supply(ies) to respective ones of the alignment electrodes 608 to thereby drive the respective alignment electrodes 608. Although the electrode support member 610 has been described above as being provided as an electrically insulative body, it will be appreciated that other configurations are possible. For example, the electrode support member 610 may be replaced with a plurality of electrically conductive support members insulated from each other and eachbiased by a predetermined voltage and contacting a different respective alignment electrode608.

[0047] As variously shown in FIGS. 6 and 7 (though labeled only in FIG. 7), the electrode support member 610 may include a plurality of first mounting holes 702 and a second mounting hole 704 formed therein. Fastener assemblies (e.g., similar to any of fastener assemblies 107 or 109) may be inserted through the first mounting holes 702 to secure the electrode support member 610 within the electron ionization source 100 (e.g., to secure the electrode support member 610 to a corresponding one of the first filament electron entrance electrode 106 or second filament electron entrance electrode 108). Similarly, the post support 604 may be secured to the electrode support member 610 by inserting a fastener assembly (not shown, but comprised of a bolt, nut and, optionally, one or more washers) provided through the second mounting hole 704 of the electrode support member 610 and a slot 604a of the post support 604 to create a bolted joint that exerts a clamping force which presses the electrode support member 610 and post support 604 against each other. Alignment of the filament 600 relative to the alignment electrodes 608 (e.g., along the y-axis) can thus be set by adjusting the position of the post support 604 on the electrode support member 610 before clamping the two bodies together.

[0048] As mentioned above, the electron ionization source 100 may optionally include a trap electrode (e.g., a metal plate, at ground potential) arranged opposite an electron source assembly 104 to collect the electrons generated by the electron source assembly 104 exiting the ionization region. In this optional embodiment, the trap electrode may be located behind the electrode support member 610 adjacent to a trap electrode window 706 (labeled in FIGS. 6 and 7, but best shown in FIG. 7). Accordingly, electrons exiting the ionization region In this case, In another embodiment, in which the electron ionization source 100 includes first and second electron source assemblies 104a and 104b, one or more alignment electrodes of the first and second electron source assemblies 104a and 104b may be used as a trap electrode while the other of the first and second electron source assemblies 104a and 104b is operated to generate the electrons.

[0049] Referring to FIGS. 6 and 8, the electron source assembly 104 includes four alignment electrodes 608 (i.e., first alignment electrode 608a, second alignment electrode 608b, third alignment electrode 608c and fourth alignment electrode 608d). Alignment electrodes 608 adjacent to one another along the x-axis are spaced apart from one another by a first distance,dl, alignment electrodes 608 adjacent to one another along the y-axis are spaced apart from one another by a second distance, d2, and alignment electrodes 608 adjacent to one another along the z-axis are spaced apart from one another by a third distance, d3.

[0050] Each of the alignment electrodes 608 may include a first portion 800 located generally behind (along the z-axis) the filament 600, a second portion 802 extending from a location relatively far (along the y-axis) from and behind (along the z-axis) the filament 600 to a location relatively close to (along the y-axis) and in front of (along the z-axis) the filament 600, and a third portion 804 extending from a location relatively far from and behind (along the z-axis) the filament 600 to a location relatively close to and in front of (along the z-axis) the filament 600. The major surface of the first portion 800 of an alignment electrode 608 is generally parallel to the x-y plane, the major surface of the second portion 802 of an alignment electrode 608 extends in a plane oblique to the x-y plane, and the major surface of the third portion 804 of an alignment electrode 608 is generally parallel to the y-z plane. In the illustrated embodiment, each of the first portion 800, second portion 802 and third portion 804 are integrally formed together (e.g., from a common plate of electrically conductive material that is cut and bent into the positions shown and described herein), but it will be appreciated that the first portion 800, second portion 802 and third portion 804 of the alignment electrode 608 may be constructed in any other suitable or desired manner.

[0051] The filament 600 is positioned so as to be located along the y-axis between alignment electrodes 608 at approximately the midpoint of the second distance, d2 (e.g., such that the shortest distance between the filament 600 and the first alignment electrode 608a or second alignment electrode 608b is about equal to the shortest distance between the filament 600 and the third alignment electrode 608c or fourth alignment electrode 608d). Additionally, the position of the filament 600 along the z-axis between alignment electrodes 608 is offset from the midpoint of the third distance, d3 in the +z direction (e.g., such that the filament 600 is closer to the leading edges 802a and 804a of the second and third portions 802 and 804 of an alignment electrode 608 than to the first portion 800 thereof, as measured along the z-axis). Optionally, the filament 600 may be positioned along the z-axis so as to be located between the first portion 800 of an alignment electrode 608 and the leading edges 802a and 804a of the second and third portions 802 and 804 thereof.

[0052] Each of the alignment electrodes 608 can be driven at a potential that is more negative than the potential at which the filament 600 is operated to generate the electron beam and,thereby, can function as a pusher electrode. Further, as constructed above, the second and third portions 802 and 804 of each of the alignment electrodes 608 are configured to focus the electron beam generated by the filament 600 when the alignment electrode 608 is driven. The focusing helps to ensure that the electron beam passes through the middle (i.e., as viewed along the y-axis) of the electrode aperture in an adjacent filament electron entrance electrode and, in the z-axis, near the nozzle 118; although, because there is a spread in emitted energies and positions with respect to the alignment electrodes 608, the position of the electron beam cannot not precisely defined.

[0053] Since the alignment electrodes are spaced apart from one another (i.e., electrically isolated from one another), the alignment electrodes 608 can be differentially driven relative to one another to steer the electron beam along the x- and y-axes. For example, if the first alignment electrode 608a and second alignment electrode 608b are driven at a potential that is more negative than that of the third alignment electrode 608c and fourth alignment electrode 608d, then the electron beam generated by the filament 600 will be deflected in the -y direction. Contrarywise, if the first alignment electrode 608a and second alignment electrode 608b are driven at a potential that is less negative than that of the third alignment electrode 608c and fourth alignment electrode 608d, then the electron beam generated by the filament 600 will be deflected in the +y direction. Similarly, if the first alignment electrode 608a and third alignment electrode 608c are driven at a potential that is more negative than that of the second alignment electrode 608d and fourth alignment electrode 608d, then the electron beam generated by the filament 600 will be deflected in the +x direction. Contrarywise, if the first alignment electrode 608a and third alignment electrode 608c are driven at a potential that is less negative than that of the second alignment electrode 608d and fourth alignment electrode 608d, then the electron beam generated by the filament 600 will be deflected in the -x direction. It will thus be appreciated that the potential at which each of the first alignment electrode 608a, second alignment electrode 608b, third alignment electrode 608c and fourth alignment electrode 608d is driven may thus be selected to deflect the electron beam generated by the filament 600 along any desired directions in the x-y plane.

[0054] Although the electron source assembly 104 has been described above as including an array of four alignment electrodes 608, it will be appreciated that more or fewer than four alignment electrodes 608 may be provided. For example, alignment electrodes 608 adjacent to one another along the x-axis may be electrically connected to one another (e.g., at each firstportion 800 and / or second portion 802 thereof), alignment electrodes 608 adjacent to one another along the y-axis may be electrically connected to one another (e.g., at each first portion 800 thereof), or the like or any combination thereof. Further, one or more of the first portion 800, second portion 802 and third portion 804 of at least one alignment electrode 608 may be electrically isolated from the other portions to be driven at a potential different from that of the other portions.

[0055] Although the arrangement of the alignment electrodes 608 relative to the filament 600 has been described in a manner that renders the alignment electrodes 608 as pusher electrodes when driven as described above, it will be appreciated that one or more of the alignment electrodes 608 may be arranged relative to the filament 600 in any suitable or known manner so as to render such alignment electrode(s) 608 puller electrodes when driven (e.g., at a potential that is less negative than the potential at which the filament 600 is operated to generate the electron beam). Accordingly, within an electrode source assembly 104, the alignment electrodes 608 may be provided as pusher electrodes, puller electrodes or a combination thereof.

[0056] As mentioned above, in an embodiment in which the electron ionization source 100 includes the first electron source assembly 104a and the second electron source assembly 104b, one or more alignment electrodes 608 of one of the electron source assemblies 104 can be a trap electrode while the other of the electron source assemblies 104 is operated to generate the electrons. In this case, one or more alignment electrodes of one electron source assembly 104 can be grounded or driven at a potential that is less negative than the potential at which a filament 600 of the other electron source assembly 104 was operated to generate the electron beam.D. Embodiments Concerning Serviceability and Configuration of the Electron Ionization Source

[0057] Conventional electron ionization sources are easily and rather quickly contaminated by analyte materials (and their byproducts) because of chemical reactions involving electron impact chemical dissociation / fragmentation reactions and / or high temperature chemical dissociation at surfaces of electrodes exposed to the ionization region. For example, surfaces of the electrodes exposed to the ionization region can become undesirably contaminated with dielectric material, electrically-conductive, or some combination thereof. Build-up of dielectric contamination material cause changes in analyzer sensitivity as the dielectric material can become electrically charged (e.g., with ion or electron charges) and lead to undesirable changes in electric potentialgradients within the electron ionization source. Build-up of conductive contaminant material can lead to electrical shorts and leakage currents between electrodes, causing undetectable changes in emission current and bias potentials that degrade the sensitivity and accuracy of the analyzer. Further, analyzers are often used in a wide variety of process conditions (e.g., characterized by a range of pressures and chemistries, each of which may vary within a single application). As described in greater detail below, embodiments of the present invention can be adapted to facilitate preventative or corrective maintenance of the electron ionization source, and to support field-configuration of the electron ionization source appropriate for process conditions with which it is used. i. Embodiments Concerning the Nozzle

[0058] As mentioned above, analyte delivered into the ionization region from the outlet of the nozzle 118 forms an analyte plume that expands predominantly along the gas delivery axis 100a and, to a lesser extent, transverse to the gas delivery axis 100a. However, a residual amount of the analyte can undesirably accumulate on the nozzle 118 (e.g., at or near the outlet thereof). In addition, since the electron beam traverses the analyte plume at a location that is very close to the outlet of the nozzle 118 to assure maximum analyzer sensitivity and minimize the chances for the analyte to thermalize and mix with background gases, the outlet of the nozzle 118 may be directly bombarded by stray electrons from the electron beam (even if focused by the alignment electrodes 608), which can undesirably generate analyte byproducts that get "baked" onto the surface of the nozzle 118 at the outlet thereof. The accumulation of analyte material, or byproducts thereof, at the outlet of the nozzle 118 (e.g., clogging of the outlet of the nozzle 118) can undesirably degrade the introduction of analyte into the ionization region. It should be appreciated that clogging can also occur simply due to condensation of the analyte material on the internal walls of the nozzle 118. This will cause a change in pressure differential and plume expansion characteristics.

[0059] In view of the above, the nozzle 118 can be removable from the main body 402 of the gas source assembly 102 (e.g., removable from the aforementioned nozzle mounting block 500). Once removed the nozzle 118 can be cleaned and reattached to the main body 402 (e.g., at the nozzle mounting block 500) or replaced with a new nozzle 118. Since the nozzle 118 can be detachably coupled to the main body 402, the gas source assembly 102 can optionally be configured to prevent analyte from leaking between the nozzle 118 and nozzle mounting block 500. For example, the threaded nozzle bore 502 and threaded nozzle body 504 may beconfigured to engage with one another in a gas-tight manner, one or more seals may be provided between the nozzle bore 502 and nozzle body 504, or the like or any combination thereof. As mentioned above, the nozzle body 504 threadedly engages with receiving threads of the nozzle bore 502. In other embodiments, other mechanisms may be used to couple the nozzle 118 to the nozzle mounting block 500, such as set screws, bayonet fittings, compression fittings, etc., are some examples of mechanisms while allowing fast removal and replacement at a factory, repair center or in the field.

[0060] Different nozzles 118 that are attachable to the main body 402 may be configured the same or differently. Configurational aspects of the nozzle 118 relate to the length of the outlet 506 (also referred to herein as "outlet length"), dimensions, diameter of the outlet orifice of the outlet 506, the shape of the outlet orifice of the outlet 506 (e.g., round, elliptical, rectangular, etc.) and the provision of one or more baffles within the outlet 506 (e.g., for flow rate control of the analyte), and the like. In one embodiment, a plurality of nozzles 118 may be attachable to the main body 402, but may vary in terms of outlet length; in this case a nozzle 118 having an outlet length that will extend suitably close to an electron beam generatable by the electron source assembly 104 may be selected to be attached to the main body 402. It will also be appreciated that the configuration of the nozzle 118 selected to be attached to the main body 402 may vary depending on one or more factors such as composition of the analyte, pressure with the ionization region, or the like or any combination thereof. ii. Embodiments Concerning the Ionization Electrodes

[0061] As mentioned above, analyte delivered into the ionization region from the outlet of the nozzle 118 forms an analyte plume that expands predominantly along the gas delivery axis 100a and, to a lesser extent, transverse to the gas delivery axis 100a. The analyte plume is fairly well collimated, and most of the molecules within the analyte plume are transported to the vacuum pump along an unrestricted path. However, collimation of the analyte plume is far from perfect and some stray analyte molecules will reach surfaces of the ionization region electrodes that are exposed to the ionization region, which can cause contamination build-up and performance degradation of the electron ionization source 100 as discussed above.

[0062] In view of the above, one or more (or all) of the ionization region electrodes discussed above with respect to FIGS. 1-4 may be replaced by an electrode assembly including a frame and a modular electrode. Generally, the frame is adapted to be mechanically coupled to other components of the electron ion source 100 by one or more fastener assemblies (e.g., any of thefaster assemblies 107 and / or 109) in the manner as discussed above. Further, the frame is adapted to be attached to, or otherwise receive or support, a corresponding modular electrode. Generally, a modular electrode can include an opening such as the first electrode aperture 106a, second electrode aperture 108a or inlet port 404, depending on whether the modular electrode is to be used as any of the aforementioned first filament electron entrance electrode 106, second filament electron entrance electrode 108 or ion exit electrode 112.

[0063] An example embodiment of an electrode assembly will now be described with respect to FIGS. 9 to 11. Referring to FIG. 9, the aforementioned first filament electron entrance electrode 106 may be replaced with an electrode assembly 900, which includes a frame 902 and modular electrode 904. The frame 902 is adapted to be mechanically coupled to other components of the electron ion source 100 by fastener assemblies 107 and 109 in the manner as discussed above. Since the electrode assembly 900 replaces the first filament electron entrance electrode 106, the modular electrode 904 includes the aforementioned first electrode aperture 106a.

[0064] The frame 902 includes upper and lower rails 906a and 906b, respectively, which are arranged and configured to receive upper and lower edges of the modular electrode 904. portions thereof, is adapted to receive and support the modular electrode 904. Generally, each rail 906a and 906b includes a lip configured to overlap with a portion of the main surface of the modular electrode 904, thereby preventing the modular electrode 904 from falling out of the frame 902 once installed. Accordingly, and with reference to FIG. 10, the modular electrode 904 may be mounted to, or removed from, the frame 902 by sliding the modular electrode 904 along the direction indicated by arrow 1000 into and out of accommodation spaces defined by the upper and lower rails 906a and 906b. The frame 902 may also include a stopper 908 arranged and configured to movement of the modular electrode 904 beyond a desired position.

[0065] Referring to FIGS. 9 and 10, the electrode assembly 900 may also include a clip 910 configured to be attached to the frame 902, e.g., at a clip mounting block 912 of the frame 902 by a faster (not shown), such as a threaded bolt or the like. When the modular electrode 904 is fully inserted into the frame 902 so as to abut against the stopper 908 (e.g., as shown in FIG. 11), the clip 910 acts to trap the modular electrode 904 within the frame 902 when the clip 910 is attached to the frame 902. Also, when the modular electrode 904 is fully inserted into the frame 902 (e.g., as shown in FIG. 11), the first electron source assembly 104a and the firstelectrode aperture 106a are arranged relative to one another as described above with respect to FIGS. 3 and 4.

[0066] In one embodiment, the frame 902 and the modular electrode 904 are each formed of an electrically conductive material and, so, when the modular electrode 904 is coupled to the frame 902, they are electrically connected to one another. In another embodiment, the frame 902 is formed of an electrically insulative material and the modular electrode 904 is formed of an electrically conductive material.

[0067] In view of the above, the modular electrode 904 can be removable from the frame 902 and, once removed, can be cleaned and reattached to the frame 902 or replaced with a new modular electrode 904. Different modular electrode 904 that are attachable to the frame 902 may be configured the same or differently. Configurational aspects of the modular electrode 904 relate to the thickness and / or material of the modular electrode 904, dimensions of the opening (e.g., the first electrode aperture 106a) formed therein, and the like. It will also be appreciated that the configuration of the modular electrode 904 selected to be attached to the frame 902 may vary depending on one or more factors such as composition of the analyte, pressure with the ionization region, or the like or any combination thereof.CONCLUSION

[0068] The foregoing is illustrative of embodiments and examples of the invention and is not to be construed as limiting thereof. Although a few specific embodiments and examples have been described with reference to the drawings, those skilled in the art will readily appreciate that many modifications to the disclosed embodiments and examples, as well as other embodiments, are possible without materially departing from the novel teachings and advantages of the invention. For example, it will be appreciated that the electron ionization source 100 may be configured according to one or more of the embodiments discussed above in section B. (Embodiments Concerning Alignment of the Nozzle to the Electron Beam), according to one or more of the embodiments discussed above in section C. (Embodiments Concerning Alignment of the Electron Beam to the Nozzle), according to one or more of the embodiments discussed above in section D. (Embodiments Concerning Serviceability and Configuration of the Electron Ionization Source), or according to any combination thereof.

[0069] It will also be appreciated that the embodiments described above in section C. (Embodiments Concerning Alignment of the Electron Beam to the Nozzle) can be used withelectron sources other than those incorporated within electron ion sources adapted to generate ions for analysis by gas chromatographs. For example, the embodiments described above in section C. (Embodiments Concerning Alignment of the Electron Beam to the Nozzle) can be used to selectively and variably steer electron beams generated by electron sources incorporated within electron ion sources adapted to generate ions for analysis by residual gas analyzers, optical emission spectrometers, or the like. Further, the embodiments described above in section C. (Embodiments Concerning Alignment of the Electron Beam to the Nozzle) can be used to selectively and variably steer an electron beam generated by an electron source incorporated within an ionization gauge (e.g., a hot cathode ionization gauge). In particular, the sensitivity of devices such as residual gas analyzers and ionization gauges is directly proportional to the trajectory length of electrons traversing an ionization region before reaching the anode. However, it can be difficult (and therefore time-consuming and expensive) to manufacture these devices to ensure that the position of electrodes therein does not appreciably change from one device to another. To reduce the variability in sensitivity in these devices, then, the embodiments described above in section C. (Embodiments Concerning Alignment of the Electron Beam to the Nozzle) can be used to selectively steer the electron beam to ensure that the length of the electron beam from the filament to the anode is within a predefined tolerance regardless of the positions of the electrodes within the device.

[0070] Accordingly, all such modifications are intended to be included within the scope of the invention as defined in the claims. For example, skilled persons will appreciate that the subject matter of any sentence, paragraph, example or embodiment can be combined with subject matter of some or all of the other sentences, paragraphs, examples or embodiments, except where such combinations are mutually exclusive. The scope of the present invention should, therefore, be determined by the following claims, with equivalents of the claims to be included therein.

Claims

Claims1. An electron ionization source comprising: a gas source assembly including a nozzle having an outlet configured to deliver an analyte material into an ionization region; an electron source assembly configured to generate an electron beam intersecting the ionization region; and a fixture configured to positionally secure the gas source assembly such that the outlet of the nozzle is aligned relative to the electron beam, wherein the fixture comprises a first jaw defining a clamping space to receive a clamping section of the gas source assembly, a second jaw movably coupled to the first jaw and configured to clamp the clamping section within the clamping space, and one or more fasteners operable to adjust the vertical position of the gas source assembly along a y-axis within the clamping space, and wherein the gas source assembly is alignable in three dimensions relative to the electron beam and to an inlet of a vacuum pump positioned downstream of the ionization region.

2. The electron ionization source of claim 1, wherein the fixture is fixed to one or more electrodes selected from the group consisting of an electron entrance electrode, an electron exit electrode, and a repelling electrode.

3. The electron ionization source of claim 1, wherein lateral reference surfaces of the clamping section and corresponding interior surfaces of the clamping space are flat and aligned in a plane parallel to at least one of the x-y, y-z, or x-z planes.

4. The electron ionization source of claim 1, wherein the gas source assembly includes a nozzle mounting block having a threaded nozzle bore, and the nozzle comprises a threaded nozzle body threadably engageable with the nozzle bore such that the position of the nozzle outlet along the z-axis is adjustable by rotation.

5. The electron ionization source of claim 1, wherein the fixture includes one or more set screws extending into the clamping space to permit z-axis adjustment of the gas source assembly.

6. The electron ionization source of claim 1, wherein the nozzle is oriented to direct analyte flow toward an inlet of the vacuum pump, and wherein the alignment is repeatable upon removal and reinsertion of the gas source assembly.

7. The electron ionization source of claim 1, wherein the clamping section of the gas source assembly is biased against the first jaw by compression of the second jaw using threaded fasteners.

8. The electron ionization source of claim 1, wherein one or more compression seals or shims are provided within the clamping space to assist in z-axis positioning of the nozzle outlet.

9. A method of adjusting a nozzle in an electron ionization source, comprising: inserting a clamping section of a gas source assembly into a clamping space defined by a first jaw of a fixture; positioning the gas source assembly within the clamping space to align an outlet of a nozzle along at least one of an x-axis, y-axis, or z-axis relative to an ionization region; engaging a second jaw with the clamping section by tightening one or more fasteners to bias the clamping section against the first jaw and secure the position of the nozzle; and orienting the outlet of the nozzle such that a gas delivery axis is aligned with a direction of an electron beam generated by an electron source assembly and / or an inlet of a vacuum pump downstream of the ionization region.

10. The method of claim 9, further comprising aligning one or more lateral reference surfaces of the clamping section with corresponding surfaces of the first jaw to repeatably position the outlet of the nozzle in the x-y plane.

11. The method of claim 9, further comprising loosening the fasteners to vertically adjust the gas source assembly within the fixture along the y-axis before re-tightening to secure the assembly.

12. The method of claim 9, further comprising rotating the nozzle within a threaded bore of a nozzle mounting block of the gas source assembly to adjust the position of the nozzle outlet along the z-axis.

13. The method of claim 9, wherein the clamping section is compressed against a reference surface of the fixture by use of a set screw or compression seal inserted into the clamping space.

14. The method of claim 9, further comprising aligning the outlet of the nozzle to be coaxial with a centerline of the electron beam or with the axis of the vacuum pump inlet.

15. The method of claim 9, wherein aligning the nozzle outlet includes translating the nozzle outlet within a fixed three-dimensional coordinate system defined by the electron ionization source.

16. The method of claim 9, further comprising removing and reinserting the gas source assembly into the fixture, wherein the outlet of the nozzle returns to a previously established alignment due to reference surface engagement.

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